1. Field of Invention
The invention relates to integrated circuit (IC) metrology and more particularly to the selection of wavelengths to be used in optical metrology measurement, processing, and/or simulation.
2. Related Art
With the current drive towards smaller geometries of IC features, feature measurement is increasingly difficult as the size of the features become smaller. However, knowledge of the dimensions of gratings or periodic structures is essential in order to determine if the dimensions of the features are within the acceptable ranges and if, for example, a particular fabrication process causes the sidewalls of the features to be tapered, vertical, T-topped, undercut, or have footings.
The characteristics of gratings or periodic structures, such as their profiles, can be determined using optical metrology. In conventional optical metrology, optical metrology data is typically obtained for a specific number of measurement points corresponding to certain wavelengths, depending on the type and manufacturer of the optical metrology device. An extensive library of profiles and spectra created with the traditional number of wavelengths can result in lengthy library creation time and extensive search time. However, the use of all or a majority of the wavelengths measurements available from the metrology device does not necessarily provide more accurate data. In some instances, the use of all the wavelength measurement data occasionally may yield an erroneous library match.